1. Field of the Invention
This present invention relates to an image processing apparatus and a method of the same, and more particularly, to an image processing apparatus and a method of the same for adjusting the saturation of an input image.
2. Description of the Prior Art
In current display apparatus, users can adjust the color saturation of an image to enhance the display of the image via an OSD (on screen display) system. Referring to FIG. 1, FIG. 2A, and FIG. 2B, FIG. 1 is a function block diagram illustrating an image processing apparatus 1 of the prior art; FIG. 2A is a schematic diagram showing portions of the lightness gain look-up table 160a in FIG. 1, and FIG. 2B is a schematic diagram showing portions of the hue gain look-up table 160b in FIG. 1. The image processing apparatus 1 includes a first color space converter 10, a hue converter 12, a first saturation converter 14, processing units 16a and 16b, multipliers 18a and 18b, a second saturation converter 20, and a second color space converter 22. The processing unit 16a stores the lightness gain look-up table 160a, as shown in FIG. 2A, and the processing unit 16b stores the hue gain look-up table 160b, as shown in FIG. 2B.
The first color space converter 10 converts an input image from RGB color space into Lab color space, wherein L represents the lightness of the input image, and a and b represent the color elements of the input image. The hue converter 12 converts the color elements a and b to the hue H of the input image, wherein the hue H of the input image is defined as
  H  =                    tan                  -          1                    (              b        a            )        .  The first saturation converter 14 converts the color elements a and b to the saturation S of the input image, wherein the saturation S is defined as S=√{square root over (a2+b2)}.
The processing unit 16a determines the lightness gain (Gain-L) in accordance with the lightness L of the input image and the lightness gain look-up table 160a. The processing unit 16b determines the hue gain (Gain-H) in accordance with the hue H of the input image and the hue gain look-up table 160b. Then, the multiplier 18a multiplies the lightness gain, Gain-L, by the hue gain, Gain-H, to get the saturation gain, Gain-S, and the multiplier 18b multiplies the saturation gain, Gain-S, by the saturation of the input image to get an adjusted saturation.
The second saturation converter 20 converts the adjusted saturation to color elements a and b. Furthermore, the second color space converter 22 converts the input image output by converter 20 from Lab color space into RGB color space.
Referring to FIG. 3A and FIG. 3B, FIG. 3A is a diagram illustrating Lab color space, and FIG. 3B is a series of diagrams respectively illustrating a saturation area at different lightness in Lab color space. As shown in FIG. 3A, in Lab color space, lightness L is controlled by height, hue H is controlled by angle, and saturation S is controlled by radius. According to the above, the image processing apparatus 1 of the prior art adjusts the saturation of the input image in accordance with the lightness gain, Gain-L, and the hue gain, Gain-H. However, as shown in FIG. 3B, a saturation area of the hue varies with different lightness of an input image. Because the cross section along the L axis of the color space of each lightness is different, and each hue (angle) corresponds to a different saturation range, if the lightness gain Gain-L is determined in accordance with the lightness of the input image, and the hue gain Gain-H is determined in accordance with the hue of the input image, it is not easy to control the level of saturation, thus causing deviation in color.
Accordingly, a scope of the present invention provides an image processing apparatus and a method of the same to solve the question mentioned above.